The differences between tree and bush can be confusing, particularly when you are facing a bush that looks a lot like a tree or vice versa. However, there is a definite difference between trees and shrubs and, although some plants blur the boundaries, in most cases it is easy determine the shape of a particular plant.
The primary characteristic that defines a plant as a tree is its size. The generally accepted tree definition, as established by the American Forests organization, is that plant that has a single vertical woody trunk, with a minimum diameter of 3 inches (7.5 cm) and 4 feet (1.2 m) High. The trunk must be perennial; that is, it can not die every winter and grow back every spring. The tree should also be at least 13 feet (4 m) tall and have a markedly extended crown.
Definition of bush
Any perennial woody plant that does not meet the minimum size requirements to be considered as a tree can be classified as a shrub. Shrubs usually have more than one vertical woody trunk, with several rising from the base. Some definitions indicate that, to be considered shrubs, they must have a height greater than 1.5 feet (45 cm) or run the risk of being considered a simple plant or creeper.